Obesity contributes to cardiovascular disease, type 2 diabetes, liver disease and increases risk for many other serious health conditions throughout life. Over the past 3 decades, obesity rates have risen dramatically accompanied by significant health disparities. In the U.S., lower-income and minority groups are at greatest risk. Since the determinants of obesity are multifactorial, multidisciplinary research is essential to consider biological, behavioral, and social determinants and their interactions. The proposed project continues to be one of the most comprehensive longitudinal studies of risk for, and consequences of, obesity, with data on growth, social circumstances, psychological functioning, sleep and physical health from infancy to adulthood. It will involve 1100 Chileans at 22 y who participated in research related to nutrition, growth and development as infants, with follow up at 5, 10, and 16 y (with adolescent data on eating behavior, fat mass, and cardiovascular risk). Participants were born during a dramatic nutritional transition, resulting in obesity prevalence rising twice as fast as it did in the U.S. At 16 y, 37.7% were over-weight or obese, with 6% in the extreme obesity range. The continuation focuses on a sensitive period for obesity, the transition to adulthood. We will determine how the following processes influence the development of obesity and related health risks: biological and social factors in infancy and childhood (Aim 1); development of health behaviors (sleep, physical activity and eating behavior) from adolescence to young adulthood (Aim 2); and mechanisms relating sleep to obesity (Aim 3). For Aim 1, we will continue our ongoing approach to understanding how early life factors (e.g., infancy weight gain, breastfeeding, parent characteristics, and social circumstance) relate to obesity and health risks. We expect that risks from early life will be modified by educational trajectories, work experience, and social relationships during the transition to adulthood. For Aim 2, we will assess continuity and change in health behaviors and how they relate to obesity, cardiovascular and metabolic risk. For Aim 3, we continue our research on the biological mechanisms relating sleep to obesity, with polysomnographic recordings in 40 overweight/obese young adults and 40 normal weight controls. Because of the study's longitudinal nature, we are positioned to unravel important questions about the direction of effects between sleep and obesity. We will also study biological and behavioral responses to sleep restriction in another subset of obese and normal weight participants (n = 80). We will assess hormonal responses, followed by 4 days of monitoring for physical activity, eating behavior and sleep. Our study is exceptional in the depth and breadth of longitudinal data from infancy to the transition to adulthood, with objective data on health behaviors in adolescence and adulthood. The study remains at the forefront of understanding the complex interactions between biology, social factors, and health behaviors as they relate to fat mass and risk for heart disease, insulin resistance, and liver disease.